The principal components of a skeletal system, for example a human skeletal system, include bones which comprise the framework for the body, cartilage which forms the connecting and supportive structures among the bones, and ligaments which bind the bones together. When a ligament becomes detached from a bone, for example due to an athletic or other injury, it is often desirable to reattach the ligament to the bone.
A number of techniques have been developed for reattaching soft tissue to a bone. Many of these techniques involve grasping the soft tissue to be reattached and maintaining it in intimate contact with the bone, thereby facilitating the natural physiological process whereby the soft tissue grows back into the bone to which the soft tissue is held in intimate contact. In this regard, the soft tissue may be grasped by one or more sutures, with the sutures being secured to the bone by a bone anchor device. The particular type of bone anchor device used to secure the sutures to the bone depends upon, inter alia, the physical characteristics of the bone at the reattachment site.
Those skilled in the art will appreciate that the structure of bone is generally characterized as either compact (i.e., the hard, dense, outside or "cortical" layer of bone), or spongy (also referred to herein as cancellous bone), which contains many small cavities which may be devoid of matter, or which may be filled with matter, e.g., marrow. Moreover, bones are also generally classified according to their shape; that is, bones are either long (as in the bones of the extremities), short (for example, bones of the wrist, ankle, and sesamoid bones), or flat (such as bones of the cranium, scapula, and ribs). In addition, certain bones, for example bones of the vertebrae, are classified as irregular.
A suture anchor device which is particularly useful in the context of flat bones is described in copending U.S. application Ser. No. 08/200,163 entitled "Methods And Apparatus For Attaching Soft Tissue To Bone". Anchor devices suitable for use with flat bones often employ a shaft portion configured to engage the cancellous bone, to thereby impede migration of the device in vivo. A head portion may be connected to the shaft portion of the device, the head portion being configured to accommodate one or more sutures. Anchoring the suture to the surface of a flat bone in this manner permits the sutures to maintain the soft tissue in intimate contact with the bone proximate the reattachment site.
The use of the aforementioned anchor devices in the context of long bones has been problematic for several reasons. For example, many long bones are devoid of the dense cancellous bone, thereby making it difficult for the shaft portion to engage anatomical matter underneath the bone surface. Moreover, the convex configuration of a typical reattachment site on a long bone often makes it difficult to use a conventional head as a suture attachment site.
Noblitt et al. U.S. Pat. No. 5,203,787 issued Apr. 20, 1993, discloses an anchor device comprising a relatively rigid elongate body having first and second ends and a central portion between the ends, the central portion including a site for attaching a suture thereto. The elongate body has a longitudinal axis associated therewith which extends through the first and second ends. The suture is attached to the central portion of the body at a point which is offset from the longitudinal axis. Thus, when the device is placed in a hole in the bone and a force having a component acting in a direction parallel to the longitudinal axis is applied to the suture, the device rotates causing the ends of the elongate body to engage the bone and prevent removal of the device and suture from the hole.
Other known devices attempt to dispose the suture anchor wholly within or underneath the bone surface, such as the "Quick Anchor".TM. bone anchor manufactured by Mitek Surgical Products, Inc. of Norwood, Mass. The Mitek Quick Anchor bone anchor includes resiliently expandable wings extending from the body of the device. The device is configured to be inserted into a bore within a bone mass using a sleeve or collar to retain the expandable wings in a retracted position during insertion. Once the device is inserted into the bore, the wings expand such that the effective size of the device exceeds the diameter of the bore. When tension is applied to the suture, the expanded wings engage the undersurface of the bone proximate the bore, much like a grappling hook.
Known suture anchor devices are unsatisfactory in several respects. For example, the aforementioned Noblitt et al. device, with its suture attachment site offset from its longitudinal axis, requires that the device be inserted into the bore in a predetermined end-to-end orientation to permit the device to properly rotate within the bone when tension is applied to the suture. Moreover, the Noblitt et al. device necessarily requires that the diameter of the bore through which the device is inserted be greater than the effective cross-sectional area of the device to permit the sutures to be inserted through the bore simultaneously with the device. The aforementioned Mitek "Quick Anchor" is similarly unsatisfactory in that, inter alia, it requires cumbersome tools and accessories for inserting the device.
Moreover, many prior art devices exhibit complex geometrical shapes which are both difficult and expensive to manufacture and which impede the natural encapsulation process in vivo, thereby increasing the risk that the device may migrate within the bone structure.